The invention concerns a microporous separator for electrical accumulators or storage batteries.
An accumulator consists of two electrodes which are immersed in an electrolyte liquid and which have an opposite electrical charge. If the accumulator is electrically charged or discharged, a chemical process takes place at the electrodes. This is accompanied by a swelling and shrinking, respectively, of the electrodes. To prevent a short circuit from occurring between the electrodes due to dendritic crystal formation after a long period of operation, for example, separators are generally disposed between the electrodes (plates).
Separators of this kind must satisfy a number of requirements. On the one hand, they must assure that any direct flow of electrons between the oppositely charged plates is effectively prevented. On the other hand, such a separator must assure a largely unhampered flow of ions between the plates. Consequently, electrically nonconductive, electrolyte-resistant materials having a high volume of open pores of the smallest possible pore radius are particularly suitable for the manufacture of such separators.
It is known to manufacture a microporous separator from a polymeric substance in a basically solid form, a salt or other substance of finely granular structure being incorporated into the polymeric material, generally in a first production procedure, and then being removed again by physical or chemical methods, so that a fine-structured polymer matrix remains. Such separators have become known on a basis of polyvinyl chloride and on a basis of rubber. These separators, however, suffer from a number of disadvantages.
Firstly, it is found that the known separator materials of this kind have a certain brittleness and fragility which limit their ability to withstand handling and working. Separator materials based on polyvinyl chloride have poor resistance to heat, and also an undesirable liberation of chlorine in various forms is frequently produced by chemical influences. Rubber separators, on the other hand, have the disadvantage that they have poor resistance to oxidation and aging.